The present invention relates to an apparatus for controlling an elevator which employs an induction motor driven by an inverter.
FIG. 8 is a circuit diagram showing an apparatus for controlling a prior-art A.C. powered elevator disclosed, for example, in Japanese Patent Application Laid-open No. 62-16994.
In FIG. 8, numeral 1 designates three-phase A.C power sources, numeral 2 designates capacitors connected to the A.C. power sources 1, numeral 3 designates converters consisting of transistors 3A to 3F and diodes 3a to 3f connected to the A.C. power sources 1, numeral 4 designates a reactor inserted to the D.C. side of the converter 3, numeral 5 designates an inverter consisting of transistors 5A to 5F and diodes 5a to 5f connected to the D.C. side of the converter 3 through the reactor 4, numeral 6 designates capacitors connected to the A.C. side of the inverter 5, numeral 7 designates a hoisting induction motor connected to the A.C. side of the inverter 5, numeral 8 designates a converter connected to the A.C. power sources 1 for an emergency stopping unit catching test (hereinafter referred to "a catching test"), numeral 9 designates a reactor connected to the D.C. side of the converter 8 for a catching test, and numeral 10 designates an inverter connected to the D.C. side of the converter 8 through the reactor 9 and connected at the A.C side to the motor 7 for a catching test.
The prior-art apparatus for controlling the A.C. powered elevator is constructed as described above, and when the elevator is operated in a normal mode, A.C. power from the A.C. power sources 1 is converted to D.C. power by the capacitors 2 and the converter 3, smoothed by the reactor 4, and converted to the A.C. power of variable voltage and variable frequency by the inverter 5 to drive the motor 7. The capacitors 6 serve to reduce the ripples of the output current of the inverter 5.
At the time of catching test for inspecting the performance of the emergency stopping unit of a safety device for an elevator, the emergency stopping unit installed in an elevator cage is operated to catch guide rails, and the motor 7 is rotated to move the cage downward. Since the cage is stopped at this time, a drive sheave tends to feed the main cable to the cage side, and finally idles with respect to the main cable. This tests whether the cage slips downward even in this state. At this time, the motor 7 needs to produce a torque of 300 to 400% of the normal elevating torque so as to overcome the frictional force between the sheave and the main cable. Therefore, at the time of catching test, the converter 8, the reactor 9 and the inverter 10 for the catching test are employed to operate in parallel with the converter 3, the reactor 4 and the inverter 5 for the normal elevation.
In the prior-art apparatus for controlling the A.C. powered elevator as described above, the converter 8, the reactor 9 and the inverter 10 are exclusively used for producing high torque at the time of catching test. Therefore, the apparatus has drawback that the arrangement is expensive.